What is Netmiko?#

Netmiko simplifies SSH management to network devices. The purposes of this library are the following:

Successfully establish an SSH connection to the device.
Simplify the execution, retrieval, and formatting of show commands.
Simplify the execution of configuration commands.
Provide a (relatively) uniform API for interacting with devices.

To install netmiko simply use pip for installation.

pip install netmiko

Netmiko has the following requirements (which pip will install for you)

Paramiko >= 2.4.3
scp >= 0.13.2
pyserial
textfsm

Then import netmiko from the Python shell to make sure the module is correctly installed.

[$] <> python3 
Python 3.8.10 (default, Mar 15 2022, 12:22:08) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import netmiko
>>>

Getting Started with Netmiko#

Import the ConnectHandler() class from the Netmiko library, creates an object, and establish an SSH connection to the remote device. The required arguments to pass in as dictionary to created object as below:

device_type
hostname or IP
username
password

The next thing that to do is retrieve the show command output from the device, the script at this point is as below:

from netmiko import ConnectHandler

# Create a dictionary 
R1 = {
 'device_type': 'cisco_ios',
 'ip': '192.168.10.11',
 'username': 'admin',
 'password': 'cisco',
 'secret': 'cisco',
}

'''calling the ConnectHandler Library [**R1] means telling python to consider 
the contents of the dictionary as key-value pairs instead of single elements.'''

net_connect = ConnectHandler(**R1)
net_connect.enable()  # device enable mode

# Sending a command into the switch --->
output = net_connect.send_command("show ip int brief")
print(output)

root@NetworkAutomation-1:~# python3 01_basic_netmiko.py

Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            192.168.10.11   YES NVRAM  up                    up
FastEthernet0/1            unassigned      YES NVRAM  administratively down down

Making Configuration Changes#

This script uses a dictionary and lists to SSH and configures multiple Cisco devices using send_config_set() method. It uses for loop to get each device from the dictionary.

from netmiko import ConnectHandler

R1 = {
 'device_type': 'cisco_ios',
 'ip': '192.168.10.11',
 'username': 'admin',
 'password': 'cisco',
 'secret': 'cisco',
}

R2 = {
 'device_type': 'cisco_ios',
 'ip': '192.168.10.12',
 'username': 'admin',
 'password': 'cisco',
 'secret': 'cisco',
}

S1 = {
 'device_type': 'cisco_ios',
 'ip': '192.168.10.10',
 'username': 'admin',
 'password': 'cisco',
 'secret': 'cisco',
}

devices = [R1, R2, S1]

for device in devices:
    print()
    print (f"Connecting to the Host {device['ip']}")
    print()
    net_connect = ConnectHandler(**device)
    net_connect.enable()

    #  Create a list of configuration commands
    config_commands = ['username admin pri 15 password cisco']
    # Pass that list to the send_config_set() method
    net_connect.send_config_set(config_commands)
    # Save running-config to startup-config by executing the save_config() method
    net_connect.save_config()

    output = net_connect.send_command('show running-config | section username')
    print(output)

root@NetworkAutomation-1:~# python3 02_multi_device.py

Connecting to the Host 192.168.10.11

username admin privilege 15 password 0 cisco

Connecting to the Host 192.168.10.12

username admin privilege 15 password 0 cisco

Connecting to the Host 192.168.10.10

username admin privilege 15 password 0 cisco

Configuration changes from a file#

This script demonstrates, how to use the method send_config_from_file() in netmiko for device configuration. Using this you will be able to fetch config from external file and push to device.

from netmiko import ConnectHandler


S1 = {
 'device_type': 'cisco_ios',
 'ip': '192.168.10.10',
 'username': 'admin',
 'password': 'cisco',
 'secret': 'cisco',
}

net_connect = ConnectHandler(**S1)

file = "config_file.cfg"

with ConnectHandler(**S1) as net_connect:
    output = net_connect.send_config_from_file(file)
    output += net_connect.save_config()

print()
print(output)
print()

root@NetworkAutomation-1:~# python3 03_config_file.py

configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
S1(config)#logging buffered 100000
S1(config)#no logging console
S1(config)#end
S1#write mem

Building configuration...
Compressed configuration from 3586 bytes to 1679 bytes[OK]
S1#

Exception handling#

The exception handling module netmiko.ssh_exception in netmiko provides some exception classes that can handle such situations, that is AuthenticationException, and will catch the authentication errors in the remote device. The second class is NetMikoTimeoutException, which will catch timeouts/connectivity issues.

from netmiko import ConnectHandler
from netmiko.ssh_exception import NetmikoTimeoutException
from netmiko.ssh_exception import NetmikoAuthenticationException

R2 = {
'device_type': 'cisco_ios',
'ip': '192.168.10.12',
'username': 'admin',
'password': 'cisco123',  # Wrong Password
}

R3 = {
'device_type': 'cisco_ios',
'ip': '192.168.10.13',  # Wrong IP Addr 
'username': 'admin',
'password': 'cisco',
}

devices = [R2, R3]

for device in devices:
    try:
        net_connect = ConnectHandler(**device)
        output = net_connect.send_command("show ip int brief")
        print(output)
        print()
    except NetmikoTimeoutException:
        print("Device not reachable ---> {}".format(device['ip']))
    except NetmikoAuthenticationException:
        print("Authentication Error ---> {}".format(device['ip']))

root@NetworkAutomation-1:~# python3 04_netmiko_exception.py

Authentication Error ---> 192.168.10.12
Device not reachable ---> 192.168.10.13

Backup device configuration#

Device configuration backup is one of the most important tasks for any network engineer. In this use case, a sample python script can be used to back up the device configuration.

from netmiko import ConnectHandler
from datetime import datetime
import time

time_now = datetime.now()
time_stamp = time_now.strftime("%d-%b-%Y")

username = "admin"
password = "cisco"


R1 = {
    "host": "192.168.10.11",
    "username": username,
    "password": password,
    "device_type": "cisco_ios",
}

R2 = {
    "host": "192.168.10.12",
    "username": username,
    "password": password,
    "device_type": "cisco_ios",
}

devices = [R1, R2]

for device in devices:
    net_connect = ConnectHandler(**device)
    print ('Initiating running cofig {}'.format(device['host']))
    sh_run = net_connect.send_command('show run')

    with open(
        device['host'] + "_"  + time_stamp, 'w') as f:
        f.write(sh_run)
        print("Backup Saved")

print ('Finished backup saving...')

root@NetworkAutomation-1:~# python3 05_backup_netmiko.py
Initiating running cofig 192.168.10.11
Backup Saved
Initiating running cofig 192.168.10.12
Backup Saved
Finished backup saving...

There are lots of additional examples here on Github.

Python for Network Engineer

What is Netmiko?